There have been many attempts at passive immunotherapy of malignant tumors, but there are only a few reports in which the administration of conventional antisera inhibited tumor growth in experimental animals or in cancer patients (see Rosenberg and Terry, Advances in Cancer Research, Vol. 25, pp. 323-388 [1977]). In most of these studies antibodies against tumor-associated antigens have been used for treatment with little success. The major reasons are the difficulties in identifying tumor-associated antigens and in preparing homogeneous antibody in large quantities by conventional methods. Development of the hybridoma technique by Kohler and Milstein (Nature, Vol. 256, pp.495-497 [1975]), coupled with the realization that cell surface antigens other than tumor-associated antigens may play a role in regulating tumor cell growth, has led to a renewed interest in experimental cancer immunotherapy centered around the use of monoclonal antibodies. Considerable effort has been, and continues to be directed towards making monoclonal antibodies against plasma membrane receptors for growth factors. It is well known that the proliferation of tumor cells is controlled by various growth factors, and it has been suggested that monoclonal antibodies against growth factor receptors, which could block access of growth factors to the receptors, might provide useful therapeutic agents. Recently Trowbridge and Domingo reported in Nature, Vol. 294, pp. 171-173 (1983), that treatment with anti-transferrin receptor monoclonal antibody inhibits tumor formation by a human melanoma cell line in athymic mice. Furthermore, monoclonal antibodies against other receptors for growth factors have been derived. With regard to the present invention it is important to note that while soma data have been published on monoclonal antibodies to epidermal growth factor receptor, to date there have been no reports showing that monoclonal antibodies to epidermal growth factor receptor inhibit tumor cell growth in vivo or in vitro.